The enamel of the teeth contains hydroxyapatite as a main component. In the oral cavity, elution of phosphate and calcium ions (decalcification) and crystallization into calcium phosphate and hydroxyapatite (remineralization) are normally at equilibrium. Fluoride ions are capable of preventing dental caries by suppressing decalcification in an acidic environment, and by facilitating crystallization of calcium and phosphate ions in a neutral environment, i.e. remineralization.
However, in the case where fluoride and calcium ions are contained in the composition in advance, such a case leads to precipitation of calcium fluoride in the composition and enlargement of the particle size thereof, so that absorption of calcium fluoride into the teeth becomes almost impossible. Accordingly, if there is a need for incorporating a calcium ion-supplying compound or an abrasive containing calcium in a composition, it is preferred to use in the composition a monofluorophosphate salt which has little interactions with calcium ions, because it can be decomposed into fluoride and phosphate ions in the oral cavity.
However, even when a monofluorophosphate salt is used, an interactive reaction occurs inevitably over time insofar as a water-soluble calcium salt coexists therewith, so that the use of a monofluorophosphate salt is still insufficient. To improve such a problem, there are known methods, for example, a method of formulating sodium pyrophosphate or polyphosphate salt (JP-A-S58-35163), a method of formulating trimagnesium phosphate (JP-A-S62-35963; Japanese Patent Publication No. 1-23404), a method of formulating zinc tripolyphosphate (JP-A-H07-544), a method of allowing soluble phosphate salt to coexist (JP-A-2003-226627). Yet there has been a problem that phosphate ions have a calcium-chelating effect and therefore the calcium ion concentration responsible for remineralization of the teeth is decreased.
Patent Document 1: JP-A-S58-35163
Patent Document 2: JP-A-S62-35963
Patent Document 3: JP-A-H01-23404
Patent Document 4: JP-A-H07-544
Patent Document 5: JP-A-2003-226627
The present invention provides a composition for oral cavity containing:    (A) a calcium ion-supplying compound which supplies calcium ions at 100 to 16000 ppm;    (B) a monofluorophosphate ion-supplying compound which supplies monofluorophosphate ions at 250 to 25000 ppm; and    (C) one or more acids selected from the group consisting of lactic acid, malic acid, and tartaric acid, and the composition has a pH of 4 to 6.2.